Conventionally, an injection molding machine includes an injection apparatus. The injection apparatus includes a heating cylinder having an injection nozzle at its front end; a screw disposed within the heating cylinder such that the screw can rotate and can advance and retreat; and a drive unit for rotating, advancing, and retreating the screw.
In a metering step, the screw is rotated whereby resin having fallen from a hopper and entered the heating cylinder is heated and melted, and is accumulated forward of a screw head. With this, the screw is retreated. Subsequently, in an injection step, the screw is advanced so as to inject the resin accumulated forward of the screw head from the injection nozzle and charge it into the cavity of a mold apparatus. In a cooling step, the resin in the cavity is cooled and solidified, whereby a disc substrate is produced as a molded product. At that time, a pattern of an information surface of a stamper disposed in the mold apparatus is transferred to the disc substrate. The mold apparatus is composed of a stationary mold and a movable mold. The movable mold is brought into contact with the stationary mold and is separated therefrom by means of a mold clamping apparatus, whereby mold closing, mold clamping, and mold opening operations of the mold apparatus are performed (see, for example, Patent Document 1).
FIG. 1 is a time chart showing operation of a conventional injection molding machine.
When a mold closing step is started at timing t1 in the mold clamping apparatus, the movable platen is advanced. When the mold closing step is completed at timing t2 upon engagement of the movable mold with the stationary mold, a pressure increasing step is started so as to increase the mold clamping force. With this operation, tie bars of the mold clamping apparatus extend, and the movable platen is advanced further by an amount corresponding to the extension.
When the movable platen is stopped at timing t3, the pressure increasing step is completed, and a mold clamping step is started, whereby a first mold clamping is performed. Simultaneously, an injection step is started in the injection apparatus, whereby resin is injected under a predetermined injection pressure.
Subsequently, at timing t4, the injection step is completed and a pressure holding step is started in the injection apparatus, whereby the pressure of the resin within the cavity is held at a predetermined holding pressure. Subsequently, in the mold clamping apparatus, the first mold clamping is ended, and second mold clamping is performed.
Then, at timing t5, the pressure holding step is completed and a cooling step is started in the injection apparatus; and in the mold clamping apparatus, third mold clamping is performed. At timing t6, the cooling step is completed in the injection apparatus, and the mold clamping step is completed in the mold clamping apparatus.
After these operations, a depressurizing and mold opening step is started in the mold clamping apparatus whereby the movable platen is retreated. When the depressurizing and mold opening step is completed at timing t7 and the movable platen is stopped, a removal step is started whereby a disc substrate is removed. At timing t8, the removal step is completed, whereby the injection molding ends.
Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2002-86507